Research On Optimization Of Design Method For Initial Support And The Timing Of Applying For Secondary Lining

Shotcrete used in tunnel construction is a kind of age-based material. After theshotcrete finished, it will take a few of days or even dozens of days to make thestrength and elastic modulus reach the final value. But most of the designers oftenignore this property when designing the initial support. This paper uses FLAC3Dsoftware to achieve the simulation of changes with age for the shotcrete parameter ofthe initial support by the cycle parameter assignment of the shotcrete. Comparing thecase that consider the hardening characteristics of the shotcrete with the case thatignore the hardening characteristics of the shotcrete by numerical simulation, we canlearn that there are no significant differences in both cases on the impact of thesurrounding rock deformation and the range of plastic zone. But the stress of theinitial support vary greatly in both cases. So we need consider the shotcrete hardeningcharacteristics when designing the initial support in tunnels. This paper makes the Vclass rock lining in100m depth as an example to elaborate that it will make thedesign more reasonable and avoid wasting construction material when considering theshotcrete hardening characteristics in initial support design.For the secondary lining, determining reasonable time to apply is the key toensure the phase of the tunnel construction and the operational long-term security.This paper uses ANSYS software to simulate the tunnels in150m,200m,250m,300m depth of the IV, V grade rock respectively. By comparing the distance from theexcavation of the tunnel face when relative sinking speed of the dome meet therailway tunnel construction specifications exactly with the distance when horizontalconvergence speed of the arch foot meet the specification exactly, we can learn thathorizontal convergence speed of the arch foot ahead of relative sinking speed of thedome to meet the specification. Through the check calculation on security and crackresistance of the secondary lining and the comparison between the deformation of thesecondary lining and its limit value, we can get a reasonable opportunity to apply forsecondary lining, in addition to the case that this will interfere the tunnel excavation construction in front.